A lightning protection system (also known as LPS) is an important design feature for modern wind turbines, due to the relative height and exposure of the wind turbine structures. In general, an LPS consists of a lightning receptor provided on a wind turbine blade, which is used to receive a lightning strike. Once hit by lightning, the receptor conducts the lightning to a ground connection via a lightning down conductor provided within the blade.
As most current wind turbine designs involve pitchable blades, or blades having relatively complicated mounting arrangements at the blade root, one of the primary issues with known LPS examples is how to conduct the lightning strike from the down conductor around the root end of the blade and to a ground connection provided at the wind turbine nacelle or hub.
An example of a known LPS system can be seen in European Patent No. EP 1 561 030, which shows what can be described as a spark gap solution. In EP 1 561 030, the lightning down conductor is passed through the external wall of the blade from the blade interior, to a conductive strip or plate provided on the external surface of the blade. A head element is provided at the exterior of the blade, closely aligned with the conductive strip, the head element coupled to a ground connection provided in the greater wind turbine structure. The system presents a spark gap between the conductive strip and the head element, irrespective of the current blade pitch angle. This ensures that a conductive path is always presented from lightning receptors in the blade through the spark gap solution to the subsequent ground connection in the wind turbine structure, bypassing the root end connection of the blade and the associated pitch system and bearings.
One issue with the spark gap solution as described above is that, as the lightning down conductor must pass through the wall of the blade body, this generally requires the drilling or cutting of a suitable hole in the wall of the blade. Such a post moulding operation can impact on the structural stability of the blade, introducing weaknesses in the vicinity of the hole, which may require additional strengthening. Furthermore, such an operation can requires additional effort in assembly, as the down conductor must passed through the hole, as well as subsequent sealing of the hole.
DE 20 2010 013535 describes an alternate lightning protection system connection method, but which does not address the problem of integration with existing LPS solutions.
It is an object of the invention to provide a wind turbine blade having a Lightning Protection System with an alternative conduction path which provides for improved performance and ease of manufacture.